Damn, do you know that pussy cat is not a good clan in UR, i don't like this clan
I love it, and know what ? This is the best clan in damage reduction, beautiful woman, lovely lady and you can blow your enemies mind with this clan

It is a ridiculous mission, but as was said earlier, you don't have to sell the cards and you don't have to go for the mission.
If you are selling cards you want to sell, to make more liquid money, then the mission is a nice bonus.
If you are selling a card, the gain is the clintz, the loss is the card. The tax is a thing, but if you're selling the card, you're okay with that.